1. Field of the Invention
The invention relates to lock pins for securing side entry turbine blade roots to mating steeples in the turbine rotor. More particularly the invention relates to an expanding lock pin for side entry turbine blades that compensates for oversize or worn pin grooves in the blade root, rotor steeple or both. The expanding lock pin expands circumferentially to fill any voids within the mating groove.
2. Description of the Prior Art
FIGS. 1-3 show a known turbine rotor, such as a steam turbine rotor 10 with an array of rotor steeples 12 and steeple pin retaining grooves 14. Turbine blade 20 is affixed to the rotor 10 by sliding the blade root 22 in the axial direction A to mate with a pair of flanking steeples 12. The turbine blade 20 has a blade root pin retaining groove 24 that is aligned above a corresponding steeple pin retaining groove 14, with each groove forming half of a generally cylindrical lock pin channel. Solid lock pin 30 having a fixed diameter and cylindrical circumferential surface 32 is sized to conform in a tight clearance fit with the opposed mating pin retaining grooves 14 and 24 that form the lock pin channel's generally cylindrical aperture surface. Upon pin 30 insertion the lock pin front axial face 34 abuts the inserted blade root 20 and its rear axial face 36 is flush with the same root. The lock pin 30 has a pin tongue 38 with a flat horizontal surface that abuts against and is retained by the next sequentially inserted blade root 22. The pin tongue ramped surface 39 provides an impact surface to hammer the pin 30 into the mating pin retaining grooves 14 and 24 to establish the tight clearance fit.
After a turbine, such as a steam turbine is in operational service it is periodically overhauled for maintenance. The old turbine blades are removed from the rotor, inspected and subsequently repaired or replaced by removing the existing lock pins. Due to turbine age wear and/or damage caused during existing lock pin removal the mating pin grooves 14 or 24 may become oversized and no longer provide a tight circumferential fit for a new known, solid lock pin 30. When the pin 30 diameter and grooves 14, 24 diameters no longer meet circumferential fit specification the pin/groove interface requires remedial repair. Known pin 30/groove 14,24 interface remediation methods include machining a new pair of grooves at a different axial location along the blade root 22 and steeple 12 interface or machining the existing grooves to a larger diameter and substituting a larger diameter oversize solid lock pin 30. The additional machining steps require additional time, expense and effort to complete the turbine rotor repair service.
Thus, a need exists in the art for a turbine lock pin that is capable of mating with corresponding blade root and rotor steeple grooves, whether or not the grooves are within dimensional specification or oversize beyond specification.
Another need exists in the art for a turbine lock pin that is capable of mating with oversized blade root and rotor steeple grooves without re-machining the existing grooves or machining new grooves.
An additional need also exists in the art for a turbine lock pin that is capable of mating with corresponding blade root and rotor steeple grooves, whether or not the grooves are within dimensional specification or oversize beyond specification, that is installed with existing familiar manufacture and repair service methods.